Response inhibition is typically considered a hallmark of deliberate executive control. In this article, we review work showing that response inhibition can also become a 'prepared reflex', readily triggered by information in the environment, or after sufficient training, or a 'learned reflex' triggered by the retrieval of previously acquired associations between stimuli and stopping. We present new results indicating that people can learn various associations, which influence performance in different ways. To account for previous findings and our new results, we present a novel architecture that integrates theories of associative learning, Pavlovian conditioning, and executive response inhibition. Finally, we discuss why this work is also relevant for the study of 'intentional inhibition'.

Performance in response inhibition paradigms is typically attributed to inhibitory control. Here we examined the idea that stopping may largely depend on the outcome of a sensory detection process. Subjects performed a speeded go task, but they were instructed to withhold their response when a visual stop signal was presented. The stop signal could occur in the center of the screen or in the periphery. On half of the trials, perceptual distractors were presented throughout the trial. We found that these perceptual distractors impaired stopping, especially when stop signals could occur in the periphery. Furthermore, the effect of the distractors on going was smallest in the central stop-signal condition, medium in a condition in which no signals could occur, and largest in the condition in which stop signals could occur in the periphery. The results show that an important component of stopping is finding a balance between ignoring irrelevant information in the environment and monitoring for the occurrence of occasional stop signals. These findings highlight the importance of sensory detection processes when stopping and could shed new light on a range of phenomena and findings in the response inhibition literature.

Purpose: To assess exposure-response relations between exposure to magnetic fields and neurobehavioral effects. Materials and Methods:Twenty company volunteers completed a neurobehavioral test battery after they moved their heads with the magnetic field absent, and while they moved their heads in the inhomogenous stray fields of 1.5 and 3.0 T MRI magnets. Results:The value of the stray fields at the position of the head of the volunteer was estimated to be 0.6 T and 1.0 T on the 1.5 T and 3.0 T systems, respectively. Exposureresponse relations were found for visual (-2.1%/100 mT) and auditory (-1.0%/100 mT) working memory, eye-hand coordination speed (-1.0%/100 mT), and visual tracking tasks (-3.1%/100 mT). Eye-hand precision, scanning speed, and visual contrast sensitivity were apparently not influenced by the magnetic field strength. Conclusion:Additional research should focus on the potential side effects of interventional MR procedures because of the exposure to strong magnetic fields of these systems. RECENT TRENDS IN DIAGNOSTIC MRI procedures include a more extensive use of interventional procedures (1-3) and the use of stronger magnets (4). Although these procedures have certain advantages, they also expose the operating teams to high static, inhomogeneous magnetic fields generated by these systems because the operating teams operate in the stray field of the magnet. Although it has been shown that reports of field-induced sensory effects in the vicinity of MRI magnets can be elicited even when the magnet is ramped down (5), the incidence of sensations of nausea, vertigo, metallic taste, and magnetophosphenes (brief flashing lights) increases with the magnetic field strength (5,6). This supports the concept of field-dependent sensory effects (7). In addition, a recent study suggested that exposure to the magnetic fields generated by a 1.5 T MRI magnet temporarily affects the subject's performance in the psychomotor and visuosensory domains, but not in the short-term memory and attention domains (8). The latter finding was supported by a study with an 8 T magnetic field (9). The affected performance in the psychomotor and visuosensory domains could potentially influence the work of operating personnel performing interventional procedures (10).In this study we evaluated exposure-response relations between exposure to magnetic fields and neurobehavioral effects. The results provide additional evidence for a causal relation between exposure and effects. MATERIALS AND METHODS Study PopulationTwenty healthy male volunteers (age ϭ 25-59 years, mean ϭ 42 years) were selected from the business unit of a company that developed and manufactured MRI magnets. The volunteers were familiar with strong magnetic fields and MRI scanners, but did not necessarily work with the scanners on a daily basis. Their education varied from secondary vocational education (N ϭ 5) to B.Sc. (N ϭ 12) and Ph.D. (N ϭ 3) levels. Exposure AssessmentAll subjects were exposed for 30 minutes in three different sessions to the stray field of the ...

The study investigates the impact of exposure to the stray magnetic field of a whole-body 7 T MRI scanner on neurobehavioral performance and cognition. Twenty seven volunteers completed four sessions, which exposed them to approximately 1600 mT (twice), 800 mT and negligible static field exposure. The order of exposure was assigned at random and was masked by placing volunteers in a tent to hide their position relative to the magnet bore. Volunteers completed a test battery assessing auditory working memory, eye-hand co-ordination, and visual perception. During three sessions the volunteers were instructed to complete a series of standardized head movements to generate additional time-varying fields ( approximately 300 and approximately 150 mT.s(-1) r.m.s.). In one session, volunteers were instructed to keep their heads as stable as possible. Performance on a visual tracking task was negatively influenced (P<.01) by 1.3% per 100 mT exposure. Furthermore, there was a trend for performance on two cognitive-motor tests to be decreased (P<.10). No effects were observed on working memory. Taken together with results of earlier studies, these results suggest that there are effects on visual perception and hand-eye co-ordination, but these are weak and variable between studies. The magnitude of these effects may depend on the magnitude of time-varying fields and not so much on the static field. While this study did not include exposure above 1.6 T, it suggests that use of strong magnetic fields is not a significant confounder in fMRI studies of cognitive function. Future work should further assess whether ultra-high field may impair performance of employees working in the vicinity of these magnets.

ALH and HVC (Grant number: L-023032) is registered at ClinicalTrials.gov (ID: NCT02649231).We would furthermore like to thank Dr. Evgeny Krupitsky for his pioneering research into ketamine as a treatment and his input into the design of the study. This paper is dedicated to the memory of our colleague Dr. David Gilhooly.